The present invention relates to lamps (stationary or portable) such as hand-held, land vehicle, boat, aircraft, etc., which can be supplied with power from a variety of power sources such as a power grid (i.e., an AC power supply), a renewable energy source, or a disposable energy source, for example, and which can use rapid start metal halide bulbs.
Presently, most portable lamps use conventional glow wire bulbs which are powered by disposable or rechargeable battery cells. Unfortunately, such conventional glow wire bulbs have a low power-to-light conversion efficiency (hereinafter "conversion efficiency"), i.e., electrical energy is converted more to heat than to visible light. Although the bulb's conversion efficiency can be increased by increasing the temperature of the glow wire of the bulb, such a temperature increase rapidly reduces the service life of the bulb. The service life/conversion efficiency relationship can be improved by filling the light bulb with heavy inert gases such as Krypton or Xenon. The light power of such conventional bulbs is typically between 0.7 and 5 watts.
Light bulbs filled with halogen-hydrogen (hereinafter "halogen light bulbs") are advantageous in that they can operate at higher temperatures without suffering an unacceptably low service life. This is due, at least in part, to a "recycling" of the high temperature glow-wire material. Specifically, tungsten from the glow wire deposited on the glass surface of the light bulb migrates back to the glow wire.
Two types of halogen light bulbs are presently available; namely, a longlife halogen light bulb and a high power halogen light bulb. The service life of the longlife halogen light bulbs is on the order of 2000 hours. During operation, the glow wire attains a temperature of approximately 2900.degree.-3000.degree. K. The average light conversion efficiency is 15-20 lumen per watt. The service life of high power halogen light bulbs is about 50 hours. During operation, the glow wire attains a temperature of about 3000.degree.-3300.degree. K. The average light conversion efficiency is 20-30 lumen per watt.
Unfortunately, halogen light bulbs have a number of problems which greatly limit their use in portable or hand held lamps. Specifically, halogen lamps are extremely sensitive to changing power supply voltages. For example, a voltage increase of 5% results in a 14% increase in light output, a 6% increase in conversion efficiency, but a 50% decrease in service life. Further, since resistivity of the tungsten filament decreases with temperature, if a fully charged battery is connected to a cold glow wire, the glow wire may burn off due to the high current. Moreover, at the end of the battery discharge period, the light output and the conversion efficiency are greatly reduced and the "color temperature" is degraded. Lastly, at the end of the service life of a halogen light bulb, unless an internal fuse is employed, a damaging arc can occur.
Halogen is commonly used in light bulbs having a power rating over 2.5 watts. Hand held lamps for professional use are usually equipped with halogen light bulbs rated at between 5 and 35 watts. The 35 watt limit is dictated by the heat loss (of about 28 watts) which must be removed without burning a user. Professional hand held lamps for underwater use (e.g., a diver lamp) can be equipped with bulbs up to 100 watts since the water can remove the extra heat generated. However, for example, a 100 watt lamp requires a heavy (almost 8 pounds) NiCad (Nickel Cadmium) battery for a one hour supply of light. In each of the above examples of halogen lamps, the light output is limited based on the total power rating of the lamp and the conversion efficiency of the lamp.
Metal halide light bulbs have a much higher conversion efficiency than other conventional bulbs, i.e., on the order of 70 to 90 lumen per watt. These light bulbs emit light by ionizing gases. Metal halide light bulbs are high pressure mercury vapor light bulbs filled with heavy metal halogens to improve the "color temperature" of the emitted light. Metal halide light bulbs are typically rated from 35 to 1000 watts. Unfortunately, metal halide light bulbs need from one to three minutes, from the time they are switched on, to reach their full output. Moreover, metal halide light bulbs are difficult to restart under "hot conditions" (i.e., when they have been operating) such as after a short interruption of the power supply.
The development of special metal halide light bulbs has been funded by the European Community/European Union. These special metal halide light bulbs can restart under hot conditions and which quickly attain full light output from the time they are switched on. For example, the bulbs ECE-D1, ECE-D2 or ECE-D2-S (also covered by the German Industrial Standard DIN 72601) have these characteristics. Specifically, these special metal halide light bulbs attain 15% of total output in about 0.5 seconds and full output in about 2 seconds. Their light conversion efficiency is about 85 lumen per watt. Special metal halide light bulbs with 35 to 50 watt power ratings are currently available. Unfortunately, the special metal halide lamps require special control and ignition conditions. Specifically, a voltage of 300 to 550 volts and a fast pulse of about 23 KV-30 KV are needed to ignite these lamps. Further, an operating voltage of about 65 V-120 V is needed. Currently available electronic control and ignition systems are complex and consequently, very expensive.
In the past, the operation of metal halide bulbs was electronically controlled with current control circuitry. With current control circuitry, a choke (i.e., an inductor or winding), located between a step-up converter and a switch network, supplies a rectangular AC current in conjunction with a lamp switch network. Transistors are switched in a phased mode, i.e., first on, second off. The inductive properties of the ignition transformer do not interfere with the current control circuitry. Unfortunately, the current control circuitry is very bulky, includes a high number of components, and is expensive.
In view of the above drawbacks of the prior art, a lamp (such as a portable, hand-held lamp, for example) having a high conversion efficiency, a reasonable service life, and a high light output (in lumen) is needed. The lamp must be able to reach full output in a short amount of time and must reliably restart under "hot conditions." To be commercially viable, the control and ignition systems of the lamp must be relatively inexpensive. Lastly, the lamp should be able to operate with a variety of power sources, such as a battery, a car or boat power supply, or an AC or DC power supply.